Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$34.27	12.477%	$38.5459	$38.55	$38.55	$38.50
Purchase #2	$156.29	10.550%	$172.7786	$172.78	$172.80	$172.80
Purchase #3	$107.32	4.296%	$111.9305	$111.93	$111.95	$111.90
Purchase #4	$201.29	5.463%	$212.2865	$212.29	$212.30	$212.30
Purchase #5	$80.51	6.129%	$85.4445	$85.44	$85.45	$85.40
Purchase #6	$6.83	3.867%	$7.0941	$7.09	$7.10	$7.10
Purchase #7	$51.34	11.788%	$57.392	$57.39	$57.40	$57.40
7 purchase totals =	$637.85		$685.4721	$685.47	$685.55	$685.40